The present invention relates generally to the field of installing hollow cylinders into cylindrical bores or openings, and in particular to a portable chilling sleeve for cooling control rod drive mechanism (CRDM) guide tube nozzles so that the diameter of the tubes can be shrunk locally and expansion fitted into a hole within a nuclear reactor vessel head.
A pressurized water nuclear reactor is divided into a lower reactor vessel with a reactor core and an upper control rod assembly, part of which can be lowered into the reactor vessel for controlling the reaction rate of the nuclear reactor. The control rod assembly contains a vertical nozzle which penetrates the upper cover of the vessel, or closure head, and houses extensions of a control rod, that can be lifted or lowered by a control rod drive mechanism (xe2x80x9cCRDMxe2x80x9d), which generally operates by some combination of electrical, electromechanical, hydraulic, or pneumatic motors or drivers.
The vertical nozzle, also called a CRDM guide tube or (xe2x80x9cCGTxe2x80x9d), is fitted into the smaller holes of the closure head, for example by the method disclosed in U.S. Pat. No. 5,516,999 to Foumier. Foumier ""999 teaches a method of immersing and shrinking an adapter, in a bath of liquid nitrogen, and then removing the adapter from the bath and inserting it into a hole in a vessel cover, which is slightly smaller than the nominal outside diameter of the adapter at ambient temperature. After the adapter warms, it expands fitting tightly within the hole.
U.S. Pat. No. 5,205,038 teaches a method of extracting a tube with a cooling coil and liquid nitrogen. The cooling coil and liquid nitrogen are introduced into the tube. The tube, which is engaged at its bottom end within a nipple, becomes disengaged after the cooling coil and liquid nitrogen cool the tube and cause thermal retraction of the tube.
U.S. Pat. No. 3,900,939 to Greacen suggests a method for plugging large diameter tubes by cooling the plug such that its diameter is sufficiently contracted to be received within the tube. Returning the plug to ambient temperature causes the plug to thermally expand to a tight fit within the tube.
U.S. Pat. No. 4,284,475 to Anthony discloses a method of installing a wear sleeve for a guide tube in a nuclear fuel assembly. The sleeve is suspended at the upper end of the guide tube. The lower portion of the sleeve is expanded into intimate contact with the guide tube. Finally, the sleeve is mechanically secured to the guide tube by a crimp, in which the sleeve and guide tube are permanently deformed, providing an interference fit between the sleeve and the tube.
U.S. Pat. No. 3,977,068 to Krips discloses a method of expanding a tubular body through the application of high pressure by means of a pressure fluid. A tube, having an outer diameter somewhat smaller than the diameter of the anchoring bore of a tube plate, can be inserted into the tube plate, and pressurized with fluid, until the length portion of the tube is expanded and there is a swaged engagement between the tube and the anchoring bore.
Although methods are generally known for providing an interference fit between two objects by adjusting pressure and temperature, portable refrigeration means are not known for nuclear fuel assembly members such as control rod guide tubes. In the industry, a CGT is bathed in a barrel of liquid nitrogen at a remote location and is then moved quickly from the liquid nitrogen bath to the closure head hole by high speed crane or manipulator. Then the CGT is dropped into the closure head or vessel cover hole. This operation must generally be performed within thirty seconds.
Therefore, it is necessary to provide a portable means of freezing a CGT so that it can be frozen locally at the point that it will reside, eliminating the need for liquid nitrogen barrels in the work area, which can be unsafe. The need for transporting a CGT quickly can also be eliminated. A portable means of freezing is also needed for removing a CGT from a closure head hole since the interference fit with the closure head hole can be reversed by a reduction in the size of the CGT.
It is an object of the present invention to provide a portable refrigerator which can be locally inserted into a hollow cylinder, such as a control rod drive mechanism guide tube.
Another object of the present invention is to provide a portable refrigerator which can accept high pressure liquefied gas, such as liquid nitrogen or other cryogenic liquid, or liquid carbon dioxide, and convert the liquefied gas to a gaseous fluid.
A further object of the present invention is to provide a portable refrigerator that can freeze and shrink the outside diameter of a control rod drive mechanism guide tube, so that it can be placed within a closure head hole having a smaller diameter than the diameter of the guide tube at ambient temperature. When the refrigerator is turned off, the guide tube warms up and an interference fit is established between the guide tube and the closure head hole.
Yet another object of the present invention is to provide a portable refrigerator that can freeze and shrink a control rod drive mechanism guide tube, so that it can be removed from the interference fit established between the guide tube and the closure head hole.
Accordingly, a chilling sleeve is provided, which is directly attached to a pump to accept a pressurized liquefied gas. The chilling sleeve is small enough that it can be inserted into a control rod drive mechanism guide tube. The chilling sleeve has high pressure and low pressure chambers so that when the liquefied gas is released through the pump, it will flow to the high pressure chamber, and can then escape through holes into a low pressure chamber surrounded by an outer wall of the guide tube, where the liquefied gas will rapidly expand into a gas that can be evacuated at a controllable rate, thereby governing the temperature of the outer wall of the guide tube. A lifting device is also provided for removing the chilling sleeve once the guide tube has been frozen and fitted or removed from a closure head hole.
In one embodiment the invention comprises a portable chilling sleeve for controlling the temperature of a hollow cylinder having an outer wall and an inner surface, thereby adjusting the size of the diameter of the outer wall. The chilling sleeve includes an upper body having a sleeve leg insertable into the hollow cylinder. The upper body also has inlet and outlet ports. A higher pressure chamber is formed within the sleeve leg and is in fluid communication with the inlet port. A lower pressure chamber is formed in operation between the sleeve leg and the inner surface of the hollow cylinder. The lower pressure chamber is separated from the higher pressure chamber by escape holes in the sleeve leg and is in fluid communication with the outlet port. The embodiment further includes pump means for regulating intake into the inlet port and exhaust out of the outlet port, wherein the rate of exhaust release controls the temperature and size of the outer wall of said hollow cylinder.
In another embodiment the invention comprises a portable chilling sleeve for reversibly reducing the outside diameter of a control rod drive mechanism guide tube, the guide tube having an inner wall with an inner surface. The chilling sleeve includes an upper body having a sleeve leg insertable into the guide tube. The body also has an inlet port in fluid communication with an inlet channel within the body. The inlet channel is connected to a higher pressure chamber surrounded by the sleeve leg. A lower pressure chamber is located in operation between the sleeve leg and the inner surface of the guide tube. The lower pressure chamber is separated from the higher pressure chamber by escape holes and is in fluid communication with an outlet port in the upper body. The embodiment further includes pump means for regulating intake into said inlet port and exhaust out of said outlet port, wherein said rate of exhaust release controls the size of the outside diameter of said guide tube.
In yet another embodiment the invention comprises a method of inserting a control rod drive mechanism guide tube through a hole in the closure head of a reactor pressure vessel. The hole has a hole diameter. The guide tube has an outer wall with an inner surface and has an outer diameter greater than the hole diameter. The method includes providing a chilling sleeve with an upper body having a sleeve leg insertable into the guide tube. The upper body has an outlet port. The upper body also has an inlet port in fluid communication with a higher pressure chamber within the sleeve leg. The sleeve leg has a projection surrounded by a first o-ring seal, and an end cap surrounded by a second o-ring seal. The sleeve leg also has escape holes located between the first and second o-ring seals adjacent the end cap. The chilling sleeve is inserted into the guide tube to form a lower pressure chamber between the sleeve leg and the inner surface of the guide tube. The lower pressure chamber is in fluid communication with the higher pressure chamber via the escape holes and in fluid communication with the outlet port. A liquefied gas is introduced into the higher pressure chamber via the inlet port and is directed into the -lower pressure chamber via the sleeve leg escape holes. The liquefied gas evaporates in the lower pressure chamber to form a gaseous fluid thereby cooling the inner surface of the guide tube and reducing the outer diameter of the guide tube to a size less than the hole diameter. The gaseous fluid is discharged from the lower chamber via the outlet port and the guide tube is inserted into the hole in the closure head.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming part of this disclosure. For a better understanding of the present invention, and the operating advantages attained by its use, reference is made to the accompanying drawings and descriptive matter, forming a part of this disclosure, in which a preferred embodiment of the invention is illustrated.